There are known adaptive cruise control systems for controlling a distance from a first vehicle to a target second vehicle travelling ahead of the first vehicle, one of which is disclosed in Japanese Patent Application Publication No. 2002-307972.
The adaptive cruise control system disclosed in the Patent Publication is installed in a first vehicle for controlling the first vehicle; the first vehicle is running on a lane of a road. The adaptive cruise control system detects another vehicle running on a lane adjacent to the running lane of the first vehicle; the detected other vehicle will be referred to as an adjacent vehicle.
The adaptive cruise control system also predicts the behavior of the adjacent vehicle, and calculates the probability that the adjacent vehicle will make a lane-change from the adjacent lane to the running lane. When it is determined that the calculated probability is higher than a predetermined threshold value, the adaptive cruise control system determines that the adjacent vehicle is likely to cut into the running lane from the adjacent lane, and selects the adjacent vehicle as a target vehicle that the first vehicle, i.e. the controlled vehicle, tracks, i.e., follows up.